This invention generally relates to ammunition ignition systems and more particularly to an ignition device for combustible cartridge cases.
Ammunition for use in tank cannons may be advantageously manufactured using a combustible case component. This minimizes the volume of spent case material inside the confined space of the tank in which such ammunition is used. The conventional combustible case cartridge comprises a projectile attached to the forward end of a cylindrical combustible case containing a propellant bed. Attached to the other end of the combustible case is a metal cartridge case head having a bayonet type primer extending from the head through the rear of the combustible case into the propellant bed.
A conventional ignitor assembly of the bayonet type is disclosed in U.S. Pat. No. 3,182,595 to Hassmann. This conventional ignitor assembly had a tubular metal body having nozzle-like flash holes through the body. This was the first patent to disclose the use of benite strands contained within the body. This benite material is essentially an extruded form of black powder. The metal tube formed a pressure vessel for the benite.
One current tank cartridge having a combustible case is the M865 cartridge. The M865 tank cartridge utilizes a typical bayonet type primer similar to the Hassman primer. This cartridge has a M123 primer head assembly connected to a strong heavy steel wall tube containing an energetic ignition material such as benite with small nozzle like holes through the wall of the tube. These holes direct the ignition flame into the propellant bed.
Current primer practice is to ignite the energetic material, i.e. benite, contained within this tube from one end and to depend on a critical development of pressure within the tube to rapidly stimulate the rate of burn of the energetic material. The rate of propagation of the burn depends primarily on the pressure. Thus, the heavy steel wall tube of the conventional bayonet primer must act as a pressure vessel to try to acheive almost instantaneous ignition throughout the tube.
The problem encountered with this bayonet primer configuration in combustible cases is that after firing the round and ejection of the metal head containing the primer from the breech of the cannon, the hot steel tube projects a long distance out of the cartridge case head and presents a serious potential hazard to personnel. During the ignition process, the primer tube becomes extremely hot. In addition, if this hot steel tube comes into contact with the combustible case of the next round of ammunition to be fired, or if such a case is dropped on the hot primer tube, the case may be ignited with disastrous results.
A solution to this problem is to provide a bayonet primer with a combustible case that is consumed during the propellant burn. One such conventional bayonet type primer is illustrated and disclosed in U.S. Pat. No. 4,770,099 to Brede et al. The Brede Patent discloses a bayonet type primer having a tube made of a combustible material filled with black powder, benite, or other initiating charge material and an electrical initiator positioned midway between the ends of the tube. A pressure container is still required as this primer utilizes strands of benite which are highly dependent upon pressure for the rate of propagation. However, ignition of the igniter charge thus takes half the time to travel to the ends of the tube as does a similar conventional primer ignited from only one end. Thus the Brede et al Patent attempts to solve the problem of igniting a long propellant bed with as much longitudinal simultaneity as possible by moving the ignition point to the center of the tube rather than one end. This design is a clever but very expensive attempt to rearrange the components of a standard M125 style bayonet primer.
Another combustible primer which contains an igniter strand of penthrite and calcium silicide is disclosed in U.S. Pat. No. 3,899,973 to Brocart. In the Brocart primer, a hollow felt like cylinder made of nitro cellulose and a latex resin binder is utilized. A long central bore through the cylinder holds a detonating fuse which comprises a cylindrical lead sheath surrounding a charge of penthrite and calcium silicide. Use of such an igniter strand housed in lead creates undesirable residual products. In addition, penthrite is an explosive with a high brisance which is very undesirable as a cartridge propellent igniter.
It is therefore a general object of the present invention to provide a combustible bayonet primer which has an unpressurized tubular housing of combustible material and has an ignition velocity on the order of at least 1000 meters per second.
It is another object of the present invention to provide an inexpensive combustible bayonet primer suitable for use in long propellant bed applications.